Hey Even, that's great! I've done a similiar thing in just vocalizing the keysound in my mind and achieved great sensations as well. I think one part of the keysound is the muscle movements that go with it ( ie. opening up the throat and the expanded belly) which helps the erotic energy move throughout the body. As Jack has said, the keysound is a 'key' to unlocking those orgasmic sensations. Then when one becomes adept like Mog and others, it just literally takes a thought to bring those sensations on and it becomes so much easier.

__________________
"Life should be fragrant, rooftop to the basement." ~ U2